This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-399222, filed Dec. 27, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a fuse circuit using capacitors as fuse elements and more particularly to a fuse circuit to attain a stable operation when a destructive/nondestructive state of the fuse element is read out.
2. Description of the Related Art
A fuse element is widely used as one means for changing the circuit configuration of a completed semiconductor device. The conventional fuse element is formed of a metal or polysilicon material and it is a general method of blowing out the fuse element by use of a laser device. However, in order to blow out the fuse element by applying laser light, it is necessary to set up a state in which the fuse element is exposed and it is impossible to blow out the fuse element after it is sealed in a package, for example.
An electrical fuse element is developed to solve the above problem. The electrical fuse element uses a capacitor or high-resistance polysilicon layer as the fuse element and high voltage is applied to or a large current is supplied to the fuse element directly from an input pin or from a control circuit inside the chip to destroy the fuse element.
In a narrow sense, a fuse element such as a high-resistance polysilicon layer which is normally set in a conductive state and made nonconductive at the time of destruction is called an electrical fuse and a fuse element such as a capacitor which is normally set in a nonconductive state and made conductive at the time of destruction is called an anti fuse in some cases. However, in a wide sense, both of the above fuse elements are called an electrical fuse in this specification.
However, the fuse circuit in the conventional system described in the above document is difficult to obtain a sufficiently large read current which permits the operation of reading out a destructive/nondestructive state to be stably performed. This is because a read current which is caused to flow to determine the destructive/nondestructive state is as small as several tenths xcexcA to several xcexcA and varies to a large extent when the capacitor used as the fuse element is destroyed.
A fuse circuit according to one aspect of the present invention comprises electrical fuse elements which are commonly connected at one-side ends; a voltage generating section which is configured to selectively apply program voltage for destroying the electrical fuse element and read voltage for reading out destructive/nondestructive states of the electrical fuse elements to a common connection node of the one-side ends of the electrical fuse elements; and a readout section which is configured to read out the destructive/nondestructive states of the electrical fuse elements from the other ends of the electrical fuse elements when the read voltage is applied to the common connection node from the voltage generating section.